POLISH-1: gridify emits canonical '='; localize litter InvalidParentGender 400 (ApiError body) + de strings

gerbil-manager-web/src/pages/WurfFormPage.tsx

@@ -1,6 +1,7 @@
 import { useMemo, useState, type FormEvent } from 'react'
 import { Link, useNavigate, useParams } from 'react-router-dom'
 import { de } from '../strings/de'
+import { errorCode } from '../api/client'
 import { createLitter, getLitter, updateLitter } from '../api/litters'
 import { listGerbils } from '../api/gerbils'
 import type { CreateLitter } from '../api/types'
@@ -49,6 +50,7 @@ export default function WurfFormPage() {
 
   const [form, setForm] = useState<FormState>(EMPTY)
   const [errors, setErrors] = useState<Partial<Record<keyof FormState, string>>>({})
+  const [submitError, setSubmitError] = useState<string | null>(null)
   const [goHomeTouched, setGoHomeTouched] = useState(false)
   const [initializedFor, setInitializedFor] = useState<string | null>(null)
 
@@ -116,9 +118,18 @@ export default function WurfFormPage() {
       expectedGoHomeDate: nn(form.expectedGoHomeDate),
       notes: nn(form.notes),
     }
+    setSubmitError(null)
     const result = await mutation.run(body)
-    if (result.ok) navigate(`/wuerfe/${result.value.id}`)
-    // On failure mutation.error drives the inline alert; run() never throws.
+    if (result.ok) {
+      navigate(`/wuerfe/${result.value.id}`)
+      return
+    }
+    // Localize the backend's parent-gender 400 by its code; else generic message.
+    setSubmitError(
+      errorCode(result.cause) === 'InvalidParentGender'
+        ? t.validation.invalidParentGender
+        : result.error,
+    )
   }
 
   if (isEdit && existing.loading) return <p className="muted">{de.common.loading}</p>
@@ -223,7 +234,7 @@ export default function WurfFormPage() {
           <textarea value={form.notes} onChange={(e) => set('notes', e.target.value)} />
         </label>
 
-        {mutation.error && <div className="alert alert--error">{mutation.error}</div>}
+        {submitError && <div className="alert alert--error">{submitError}</div>}
 
         <div className="form-actions">
           <button type="submit" className="btn btn--primary" disabled={mutation.pending}>